[PATCH bpf-next 06/18] bpf: Prepare architecture JIT support for stack arguments

Yonghong Song
2026-04-24T17:15:09Z

Add bpf_jit_supports_stack_args() as a weak function defaulting to
false. Architectures that implement JIT support for stack arguments
override it to return true.

Reject BPF functions and kfuncs with more than 5 parameters at
verification time if the architecture does not support stack
arguments.

Acked-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
include/linux/filter.h | 1 +
kernel/bpf/btf.c | 8 +++++++-
kernel/bpf/core.c | 5 +++++
kernel/bpf/verifier.c | 5 +++++
4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index b77d0b06db6e..911205dd670e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1163,6 +1163,7 @@ bool bpf_jit_inlines_helper_call(s32 imm);
bool bpf_jit_supports_subprog_tailcalls(void);
bool bpf_jit_supports_percpu_insn(void);
bool bpf_jit_supports_kfunc_call(void);
+bool bpf_jit_supports_stack_args(void);
bool bpf_jit_supports_far_kfunc_call(void);
bool bpf_jit_supports_exceptions(void);
bool bpf_jit_supports_ptr_xchg(void);
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index cfb35a2decf6..fa4b971c5289 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7890,8 +7890,14 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
tname, nargs, MAX_BPF_FUNC_REG_ARGS);
return -EINVAL;
}
- if (nargs > MAX_BPF_FUNC_REG_ARGS)
+ if (nargs > MAX_BPF_FUNC_REG_ARGS) {
+ if (!bpf_jit_supports_stack_args()) {
+ bpf_log(log, "JIT does not support function %s() with %d args\n",
+ tname, nargs);
+ return -ENOTSUPP;
+ }
sub->incoming_stack_arg_depth = (nargs - MAX_BPF_FUNC_REG_ARGS) * BPF_REG_SIZE;
+ }

/* check that function is void or returns int, exception cb also requires this */
t = btf_type_by_id(btf, t->type);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index ec8523e6e4eb..7522b3d7b267 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3217,6 +3217,11 @@ bool __weak bpf_jit_supports_kfunc_call(void)
return false;
}

+bool __weak bpf_jit_supports_stack_args(void)
+{
+ return false;
+}
+
bool __weak bpf_jit_supports_far_kfunc_call(void)
{
return false;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e041c182c614..0ba140dabe93 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12254,6 +12254,11 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
MAX_BPF_FUNC_REG_ARGS);
return -EINVAL;
}
+ if (nargs > MAX_BPF_FUNC_REG_ARGS && !bpf_jit_supports_stack_args()) {
+ verbose(env, "JIT does not support kfunc %s() with %d args\n",
+ func_name, nargs);
+ return -ENOTSUPP;
+ }

/* Check that BTF function arguments match actual types that the
* verifier sees.
--
2.52.0